I have a 1946 Cape Cod in Indiana with an unvented attic. I want to insulate the house with foam. Should I use open or closed cell foam?

Asked by David Mills
Indianapolis, IN

The house has a basement and an unvented crawl space with a center vent stack that is open to the roof's ridge. There is a 5" HVAC duct open in the crawl. In the summer the upstairs is hot and in the winter it is cold. The house has knee walls with fiberglass and the vapor barrier is on the attic side. The second floor flat ceiling space had 10" to 24" of cellulose installed with the new roof. Fiberglass-wrapped ductwork is in the knee wall attic space. I am getting ready to have open cell foam blown through the brick into the first floor walls. How should I insulate the rest of the house?


Kevin Holdridge

Answered by Kevin Holdridge

Charlotte, NC

KDH Residential Design, LLC

December 20, 2010

Closed cell foam acts as an air barrier and a vapor retarder, therefore should be used in unvented roof assemblies in colder climates. Closed cell foam has a lower vapor permeability and higher thermal resistance than open cell foam.

For more information:

Read Steve Saunders' Q&A "I'm converting my attic into a non-vented conditioned space. Should I use open cell or closed cell foam to insulate?"

Tagged In: spray foam, attic insulation

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